As is already known from French patent application No. 2,955,165 filed by the applicant, such a motor vehicle powertrain comprises a thermal engine with a shaft connected to a variable-speed transmission device including an epicyclic gear train with a sun gear and a crown connected each to the thermal engine shaft by a controlled coupling and to a fixed part of the powertrain by a one-way automatic coupling, and a planet gear carrier transmitting the speed variation to the drive axle of the vehicle through a transmission track.
In order to increase the speed variation capacity when the vehicle is driven by the electrical machine, the applicant has combined the variable-speed transmission device of the aforementioned document with another epicyclic gear train connecting the engine epicyclic gear train to a transmission track for motion transmission to the drive axle of this vehicle, as described in French patent application No. 2,962,697 filed by the applicant.